The invention relates to an electrolytic foil capacitor comprising a metal housing which is open on one side and which is provided on this side with a seal formed of an electrically insulating material. The housing contain, wound around a metal pin, an assembly of a strip of an anode foil provided with a dielectric oxide layer by forming, two or more strips of separator foils impregnated with electrolyte liquid, and a strip of a cathode foil, which are wound together to form a roll. The metal pin is led outwards through the seal on the open side of the housing, and the cathode foil is provided with a first tag protruding from the roll, which is tag being mechanically and electrically connected to the housing.
In United States patent specifications U.S. 3,754,113 such a capacitor is disclosed, in which the anode foil is mechanically and electrically connected to the metal pin via the short side of the strip and the metal pin is provided with an axial lead wire, the cathode foil being provided with a tag projecting from the roll, which tag is mechanically and electrically connected to the housing on the bottom side of the housing, and the latter is provided with a second lead wire.
High-capacitance anode foils for the manufacture of electrolytic foil capacitors having a large product of operationing voltage and capacitance have a surface which is substantially enlarged by pores. Such a foil is brittle and cannot be reliably connected to the metal pin by means of the customary techniques such as cold welding or ultrasonic welding. Cementing using an adhesive also leads to problems in the realisation of an electrically conductive connection.
Another problem which may occur in the known electrolytic capacitors is caused by the fact that the first part of the anode foil is not surrounded by the cathode foil. This leads in certain frequency ranges to a decrease of the capacitance and an increase of the electric losses.
Since the connections of the anode foil and the cathode foil are asymmetrical, the capacitor has a relatively large self-induction (ESL). This is undesired with respect to application at high frequencies.
An additional problem is the relatively high equivalent series resistance which is caused by the fact that a long strip of anode foil is electrically connected to the anode pin at one end only.